This invention relates to an optical recording medium and a method of fabricating same. More particularly, the present invention is directed to a rewritable optical recording medium of a phase-change type which does not require initialization or which requires only a short time for initialization.
There is conventionally known a phase-change optical recording medium which utilizes phase changes between a crystalline phase and an amorphous phase and is capable of recording, reproducing and erasing information by the application thereto of a laser beam. Such a recording medium permits overwriting with a single beam and has compatiblity with CD-ROM and CD-R, and is expected to be utilized as DVD-RAM medium.
In phase-change type optical recording media, the recording layer generally assumes amorphous state in a recorded condition and crystalline state in an erased condition. Thus, the recording media are required to be initialized after the recording layer has been formed. The initialization is carried out by a thermal treatment such as by irradiation with a laser beam. The initialization requires a process time of more than 30 seconds and causes a reduction of throughput. Further, costs of apparatuses for producing the optical recording media increase.
JP-A-H09-161316 discloses an optical recording medium having a crystallization accelerating layer formed between a substrate and a recording layer and made of SbxTe(1xe2x88x92x) where x is a number greater than 0.3 and smaller than 0.5. The accelerating layer is described as serving to shorten a time required for initialization.
JP-A-H11-96596 discloses an optical recording medium having a crystallization accelerating layer formed between a substrate and a recording layer and made of a Ge-Te-Sb or Ge-Te-Sb-Bi alloy having a relatively low crystallization temperature. The accelerating layer is selected from Bi, Sb, Bi compounds and Sb compounds. The accelerating layer is described to permit omission of initialization.
According to the known techniques, initialization becomes unnecessary only when the recording layer has a low crystallization temperature and is easily crystallized. The use of a recording layer having a low crystallization temperature, however, has a problem because storage stability of the amorphous recorded marks.
In accordance with one aspect of the present invention, there is provided an optical information recording medium, comprising a substrate, a first dielectric layer provided on said substrate, a recording layer provided on said first dielectric layer, a second dielectric layer provided on said recording layer, a light reflection and heat dissipation layer provided on said light reflection and heat dissipation layer, and a crystallization accelerating layer provided in contact with at least a portion of said recording layer and made of a material comprising a substance selected from the group consisting of Bi, Bi-containing compounds, Al, Al-containing compounds, In, In-containing compounds, Tl and Tl-containing compounds.
In another aspect, the present invention provides a method of fabricating an optical information recording medium, comprising the steps of forming a first dielectric layer on a substrate, forming a recording layer on said first dielectric layer, forming a second dielectric layer on said recording layer, forming a light reflection and heat dissipation layer on said light reflection and heat dissipation layer, and forming a crystallization accelerating layer in contact with at least a portion of said recording layer, said crystallization accelerating layer being made of a material comprising a substance selected from the group consisting of Bi, Bi-containing compounds, Al, Al-containing compounds, In, In-containing compounds, Tl and Tl-containing compounds.
It is an object of the present invention to provide an optical recording medium which does not require initialization or which requires only a short time for initialization.
Another object of the present invention is to provide an optical recording medium which has good storage stability of amorphous marks.